Duchenne Muscular Dystrophy (DMD) in both humans and dogs is a fatal, X-linked, recessive muscle disease caused by a lack of dystrophin due to deletions or mutations in the dystrophin gene. The disease is inherited in a recessive pattern suggesting that gene therapy could offer an effective treatment if methods can be found to replace the defective gene in muscle. Studies in the mouse model ofDMD (mdx) have shown that delivery of mini-dystrophin adeno-associated viral (AAV) vectors, which display a remarkable ability to transduce skeletal muscle vectors to adult mdx muscle results in correction of most, but not all, features of dystrophy. Prior to launching into clinical trials with this vector system, data in a large animal model, which more closely reflects the disease phenotype in humans, are needed to assess the safety and effectiveness of this approach. Three specific hypotheses will be tested: 1) that an increase in muscle fiber integrity and function can be achieved by targeted direct injection of AAV vectors containing truncated canine dystrophin genes; 2) that wild type satellite cell transfer and vascularized muscle transplants will result in successful transfer and persistence of wild type satellite cells for the correction of the DMD phenotype; and 3) that seeding of wild type satellite cells will occur from normal to diseased muscle. Aims 1 and 2 will be conducted in recipients of marrow grafts to avoid potential rejection of wild type cells by the immune system. The canine model of DMD that is clinically and pathologically similar to human DMD will be used. These studies will provide baseline data for the development of a phase I clinical AAV gene therapy trial for DMD (Project 1). The long-term obiectives of the proposed research are to determine if direct AAV-dystrophin gene and cellular itransplant delivery ameliorates and reverses dystrophic pathology in xmd muscle and if this leads to normal myofiber morphology, histology, cell membrane integrity and function. The development of new therapies in the canine model could have immediate impact on the treatment of DMD patients.